Touch screens are present in many different types of common modern electronic devices, such as smart phones, tablet computers, portable music and video devices, personal digital assistants, portable gaming devices, computer systems, and so on. In these electronic devices the touch screen is part of the user interface of the device. The touch screen typically includes a visual display and touch sensors or a touch panel. A touch controller is coupled to the touch screen and operates to process signals from the touch panel to detect inputs by a user. The touch panel includes some sort of transparent sensor array, such as an ultrasonic, resistive, vibration or capacitive sensor array, or a combination thereof, which is attached to or formed as an integral part of the visual display, which may be a liquid crystal display (LCD), for example.
In operation, a user touches a surface of touch panel or “hovers” his or her finger or a suitable object above the touch panel, and the sensor array generates corresponding electronic sensor signals that are provided to the touch controller. From these sensor signals, the touch controller determines the type of “touch event” or “hover event” input by the user to the touch panel and provides this information to processing circuitry in the electronic device. The processing circuitry operates in response to this information to allow a user to control the electronic device or an application running on the processing circuitry through these touches of the touch panel. Many current touch panels are capable of detecting multiple touch and hover events simultaneously, and may also detect gesture events that are similar to hover events except involve a predefined motion of a user's finger.
A typical sensor array of a touch panel is a capacitive sensor array including a number of force or drive lines and orthogonally arranged sense lines. These lines are made from suitable conductive materials, such as Indium Tin Oxide (ITO), which are transparent to visible light. In the touch panel, the drive lines are formed on one layer of the sensor array structure and the sense lines formed on another layer of the structure, with these layers being separated by a transparent insulating material such as glass. The overlap of the drive lines and the orthogonally arranged sense lines with the insulating material between forms an array of capacitive sensor nodes or sensors. In operation, a drive signal, which is typically a periodic waveform such as a pulse train, is applied successively to the drive lines. As the drive signal is applied to a given drive line, the capacitive coupling between that drive line and the sense lines through the corresponding sensor nodes results in capacitive coupling of the drive signal to the sense lines to thereby generate sense signals on the sense lines responsive to the drive signal.
The value of the sense signal generated on each sense line is a function of the capacitive coupling between that sense line and the drive line receiving the drive signal. This capacitive coupling changes in response to a user's finger, or other touch device, being proximate the sensor nodes formed at the overlap of the drive and sense lines. This change in capacitive coupling of the drive signal to the sense lines will result in a change in the sense signal generated on the sense lines, and in this way the sense signals indicate whether a user's finger or other touch device is adjacent a given sensor node in the touch panel.
In operation, to scan the entire sensor array of a touch panel the drive signal must be applied to each drive line and the resulting sensor signals on the sensor lines sensed and processed to detect touch or hover events. As a result, the time it takes to scan the entire sensor array is function of the number of sensors in the array. A response time is determined by the time it takes to scan an array and process the corresponding sense signals to detect touch and hover events on the touch panel. If the response time of a touch panel is too slow this will manifest itself as an unpleasant experience for the user of the electronic device containing the touch panel. The user will notice undesirable delays between inputting a touch or hover input and the electronic device responding to this input. The size of a touch panel is the number of sensors in the touch panel and as the size increases the response time typically increases. This is true because a larger size touch panel has more sensors and thus more drive and sense lines to control. As a result, a method of scanning a touch panel having a given size suitable for an electronic device such as a smart phone may be unsuitable for larger size touch panels in devices such as tablet computers, notebook computers, and televisions. Accordingly, there is a need for improving the way in which touch panels are scanned to ensure the response times of the touch panels are acceptable for desirable operation of the associated electronic device.